This project involves structure studies of soluble extracellular domains of a receptor-ligand pair of IgG superfamily molecules, one from T-cell and one from B-cell, that interact to enhance antibody production in response to antigen presentation. Interference with this interaction may permit targeted immunosuppression for specific therapeutic purposes and structural information is needed to reveal the nature of the CTLA4-B7-1 interaction and inform the design of small molecule effectors.